JPH07152267A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce the scratching, shaving, etc., of an intermediate transfer body or a transfer member and to enhance durability and transfer efficiency by providing a protective layer on the surface of a contact transfer member used for a secondary transfer. CONSTITUTION:As a transfer member 25 for the secondary transfer, an elastic transfer roller 25 using a foamed EDPM 27 whose surface layer is coated with a polyurethane elastomer to provide a surface protective layer 28 is used. The surface protective layer 28 is a thin layer coat, so that the hardness of the transfer roller 25 is the same as that is used in the case of a foamed EPDM single layer. Thus, reduction in the outside diameter caused by the shaving of the transfer roller 25 and the oozing out of oil from the EPDM layer 27 can be decreased up to about 1/10 compared with the case where the transfer roller of the foamed EPDM single layer is used and further, fluctuations in the resistance value of the transfer roller 25 caused by the passage of a paper sheet can be lessened. Further, it is unnecessary that the hardness of the surface layer of the transfer roller 25 can be made high, so that the intermediate transfer body 20 can not be shocked unnecessarily and its life can not be shortened as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type printer / printer.
The present invention relates to an image forming apparatus such as a copying machine or a facsimile.

More specifically, a transferable image (toner image) is formed on the first image bearing member by an appropriate image forming process, the image is transferred onto the intermediate transfer member (primary transfer), and then the intermediate image is transferred. A method in which a second image bearing member is pressed against a transfer member with a transfer member to transfer the image on the intermediate transfer member to the second image bearing member side (secondary transfer) to output an image formed product (copy / print). Image forming apparatus.

In the above, the first image carrier is, for example, an electrophotographic photoreceptor, an electrostatic recording dielectric, a magnetic recording magnetic body, or the like.

The image forming process for the first image carrier is, for example, an electrophotographic process, an electrostatic recording process, a magnetic recording process or the like.

The intermediate transfer member and the transfer member are roller-shaped bodies (drum-shaped bodies), belt-shaped bodies and the like.

The second image carrier is, for example, a transfer material, recording paper, printing paper, card, envelope, postcard, etc., and the material is not limited to paper.

[0007]

2. Description of the Related Art As described above, an image forming apparatus using an intermediate transfer member is an intermediate transfer device that repeats the steps of forming a transferable image on a first image carrier and primary transferring the image to the intermediate transfer member. Obtaining a color image or a multicolor image by collectively forming a color image or a multicolor image composed of developers of a plurality of colors on the body and then secondarily transferring the images to the second image carrier at once. A color image forming apparatus or a multicolor image forming apparatus for outputting an image formed product in which a plurality of component color images of color image information or multicolor image information are sequentially laminated and transferred to synthesize and reproduce a color image or a multicolor image. Alternatively, it is effective as an image forming apparatus provided with a color image forming function and a multicolor image forming function, and the misregistration (color misregistration) of each component color image.
It is possible to obtain an image without.

[0008]

However, there are some problems. First, conventionally, there was only a contact state of a combination of a photosensitive drum as a first image carrier and a transfer roller as a contact transfer member, which has a relatively small frictional resistance, but an image forming apparatus using an intermediate transfer body. However, since the elastic members such as the intermediate transfer member and the transfer roller are in contact with each other, the deterioration of wear of the intermediate transfer member or the transfer roller tends to be accelerated.

Further, when the separating means is provided so that the intermediate transfer member and the transfer roller do not always contact each other,
If the hardness difference between the surface layer of the intermediate transfer body and the transfer roller is large, there is a problem that each time the contact is made to occur, partial deterioration is promoted, or resistance changes due to stress on the elastic body layer when making contact. .

Further, since the primary transfer of the image from the first image carrier to the intermediate transfer member and the secondary transfer of the image from the intermediate transfer member to the second image carrier and the double transfer are repeated, the whole is repeated. However, there is also a problem that the transfer efficiency of is low.

Therefore, the present invention solves the above-mentioned problems in the image forming apparatus using the intermediate transfer member, that is, reduces the scratches and abrasions of the intermediate transfer member or the transfer member, and enhances the durability. The purpose is to improve efficiency.

[0012]

According to the present invention, after transferring an image formed on a first image carrier onto an intermediate transfer member,
In the image forming apparatus for transferring the image on the intermediate transfer member to the second image carrier side by pressing the second image bearing member to the intermediate transfer member with the transfer member, a surface protective layer may be provided on the transfer member. A characteristic image forming apparatus.

[0013]

When a transfer member having no surface protection layer is used, it is possible to reduce the outer diameter of the transfer member due to abrasion of the transfer member or oil bleeding from the inner layer of the transfer member by providing the surface protection layer on the transfer member. It is possible to reduce the resistance value of the transfer member to about 1/10, and it is possible to suppress the fluctuation of the resistance value of the transfer member due to the passing of paper. Further, since the hardness of the surface layer of the transfer member is not increased, the intermediate transfer body is not subjected to an excessive impact and the life of the intermediate transfer body is not shortened.

By constantly contacting the transfer member with the intermediate transfer member, the transfer member and the intermediate transfer member due to a shock or the like at the time of contact / separation in an apparatus configured to control the transfer member to contact / separate with respect to the intermediate transfer member at a predetermined time. Although body abrasion and scratches can be reduced, in this case, in order to prevent image transfer from the intermediate transfer member to the transfer member during primary transfer of the image from the first image carrier to the intermediate transfer member, When the transfer member is configured to apply the image adhesion preventing bias to the transfer member, if the transfer member is conductive, the primary transfer current flows from the intermediate transfer member to the transfer member, and the first image carrier The primary transfer efficiency from the intermediate transfer body to the intermediate transfer body decreases, but by forming an insulating layer on the surface layer of the transfer member as a surface protection layer to prevent current flow, the primary transfer current leaks to the transfer member. Can be prevented Improvement of the efficiency is possible.

Further, by providing a surface protective layer on the transfer member, it is possible to impart releasability and prevent contamination of the transfer member.

When an image is formed on the first image carrier with a substantially spherical toner, the spherical toner has a small area in contact with the roller surface or the like, so that the releasability is high and the image is the first image at the time of primary and secondary transfer. Almost no residue remains on the image bearing member or the intermediate transfer member, so there is little occurrence of voids during transfer. The voids in the transfer of the image are largely affected by the surface hardness of the transfer member. However, by using the spherical toner, a material having a high hardness such as a PFA tube can be used as a coating material (surface protective layer) of the transfer member.

[0017]

【Example】

<Embodiment 1> (FIGS. 1 to 3) FIG. 1 is a schematic configuration diagram of an apparatus according to the present embodiment. The apparatus of this embodiment is a color image forming apparatus (copier or laser beam printer) using an electrophotographic process. In this embodiment, a medium resistance elastic roller (intermediate transfer roller) 20 is used as an intermediate transfer member.

A reference numeral 1 designates a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) which is repeatedly used as a first image bearing member, and has a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow. ) Is driven to rotate.

The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a primary charger (corona discharger) 2 in the course of rotation, and then an image exposing means (not shown) (color separation of color original image-bonding). The image exposure optical system, a scanning exposure system by a laser scanner that outputs a laser beam modulated in response to a time series electric digital pixel signal of image information, etc. An electrostatic latent image corresponding to a color component image, for example, a magenta component image is formed.

Then, the electrostatic latent image is developed by the first developing device 41 (magenta developing device) with the magenta toner M of the first color. At this time, the second to fourth developing latent image devices 42
43/44 (Cyan / Yellow / Black developing units)
Is activated-off and does not affect the photosensitive drum 1,
The magenta toner image of the first color is not affected by the second to fourth developing units 42 to 44.

The intermediate transfer roller 20 is rotationally driven in the counterclockwise direction indicated by the arrow at the same peripheral speed as the photosensitive drum 1. The intermediate transfer roller 20 of this embodiment has a pipe-shaped core metal 21 as shown in the cross-sectional model view showing the layer structure of FIG.
And an elastic layer 22 of medium resistance formed on the outer peripheral surface thereof.

The medium resistance elastic layer 22 of the intermediate transfer roller 20 of this embodiment is made of an elastic material such as silicone rubber, Teflon rubber, chloroprene rubber, urethane rubber, EPDM, or the like.
It is a solid or foamed meat layer in which a metal oxide such as carbon or zinc oxide is mixed and dispersed to adjust the electric resistance value (volume resistivity) to a medium resistance of 10 ⁵ to 10 ¹¹ Ω · cm.

Further, the image forming apparatus of the present embodiment uses the A4 size transfer material 24 as the second image carrier by feeding it vertically, and the peripheral length of the intermediate transfer roller 20 is the A4 size transfer material 24. Is set to 314 mm (roller outer diameter 100 mm), which is slightly larger than the length. The elastic layer 22 has a wall thickness of 8 mm and an Asker C hardness of 20 ° to 40 °.

Thus, the magenta toner image of the first color formed and carried on the photosensitive drum 1 passes through the nip portion N1 (primary transfer portion) between the photosensitive drum 1 and the intermediate transfer roller 20, By the electric field formed by the primary transfer bias applied from the power source 61 to the intermediate transfer roller 20,
Intermediate transfer is sequentially performed on the outer peripheral surface of the intermediate transfer roller 20.

The surface of the photosensitive drum 1 on which the transfer of the magenta toner image of the first color onto the intermediate transfer roller 20 is completed is
It is cleaned by the cleaning device 14.

Similarly, a second color cyan toner image, a third color yellow toner image, and a fourth color black toner image are sequentially formed on the photosensitive drum 1, and these NATO images are sequentially intermediate-transferred. A composite color toner image corresponding to a target color image is formed on the intermediate transfer roller 20 by superimposing and transferring the toner images of the first to fourth colors on the roller 20.

The toners of the first to fourth colors are non-magnetic one-component toners having a volume average particle size of 5 to 8 .mu.
A negative polarity toner of -18 μc / gr was used.

The primary transfer bias for sequentially superposing and transferring the toner images of the first to fourth colors from the photosensitive drum 1 to the intermediate transfer roller 20 is applied from the bias power source 61 with the polarity (+) opposite to that of the toner. It The applied voltage is +2 kV to +5 kV in this embodiment.

Reference numeral 35 is an intermediate transfer roller cleaner, and 25 is a transfer roller as a transfer member. In the process of sequentially transferring the toner images of the first to fourth colors from the photosensitive drum 1 to the intermediate transfer roller 20, four times in sequence. The intermediate transfer roller cleaner 35 and the transfer roller 25 are separated from the intermediate transfer roller 20 by shift means (not shown).

The transfer (secondary transfer) of the composite color toner image superposed and transferred onto the intermediate transfer roller 20 to the transfer material 24 as the second image carrier is carried out by the transfer roller 25 which has been separated so far. The intermediate transfer roller 20 by the shift means
The transfer material 24 is separated and fed by the paper feed roller 10 from the paper feed cassette 9 by the paper feed cassette 9, and the contact nip portion N2 (secondary transfer roller) between the intermediate transfer roller 20 and the transfer roller 25 is fed by the registration roller 11. The secondary transfer bias is fed to the transfer unit) at a predetermined timing, and at the same time, the secondary transfer bias is supplied to the bias power source
Applied to the transfer roller 25. The secondary transfer bias causes the synthetic color toner image to be transferred from the intermediate transfer roller 20 to the transfer material 24.

The transfer material 24 that has received the toner image transfer is separated from the intermediate transfer roller 20 and is fixed by the guide 13 to the fixing device 15.
And is heated and fixed. Reference numerals 16 and 17 denote a heat roller and a pressure roller of the fixing device 15.

After the image transfer onto the transfer material 24 is completed, the transfer residual toner on the intermediate transfer roller 20 is removed by cleaning by the intermediate transfer roller cleaner 35 contacting the roller 20 by the shift means.

The transfer roller 25 as a transfer member is supported below the intermediate transfer roller 20 by a bearing portion of the shift means in parallel with the intermediate transfer roller 20, and is lifted by the shift means at the time of secondary transfer. Intermediate transfer roller 20
The secondary transfer portion N2 is formed between the intermediate transfer roller 20 and the lower surface of the intermediate transfer roller 20 with a predetermined pressing force.

The peripheral speed of the intermediate transfer roller 20 is 1.
It is rotationally driven in the clockwise direction indicated by the arrow at a peripheral speed of 01 times. This is to prevent a hollow portion during image transfer.

The transfer roller 25, as shown in FIG. 3, has carbon dispersed on the core metal 26 and has a resistance value of 10 ¹⁰ to 1 1.
The elastic layer 27 of foamed EPDM controlled to 0 ¹¹ Ω · cm is formed to have a wall thickness of about 5 mm, and titanium oxide is dispersed as a surface layer 28 on the outer periphery thereof to have a resistance value of 10 ¹⁰ to 10 ¹³ Ω ·.
cm, polyurethane elastomer 10-20μ
m is coated in a thin layer. Since the surface protective layer 28 is a thin layer coat, the hardness of the transfer roller 25 is the foamed EPD.
There is no difference from the case of M single layer.

As described above, in this embodiment, as the transfer member 25 for secondary transfer, a foamed EPDM having a surface protective layer 28 coated with a surface layer of polyurethane elastomer.
Since the elastic transfer roller 25 using No. 27 is used, the reduction of the outer diameter due to the abrasion of the transfer roller 25 or the exudation of the oil from the EPDM 27 layer is reduced to 1/10 as compared with the case of using the transfer roller of the foamed EPDM single layer. It was possible to reduce it to a certain extent, and it was also possible to suppress fluctuations in the transfer roller resistance value due to the passage of paper. Further, since the hardness of the surface layer of the transfer roller is not increased, the intermediate transfer body 20 is not given an excessive impact, and the life of the intermediate transfer body 25 is not shortened.

<Embodiment 2> (FIG. 4) FIG. 4 is a schematic diagram of the apparatus of this embodiment. In the apparatus of the first embodiment, the transfer roller 25 is brought into contact with the intermediate transfer roller 25 at the time of the secondary transfer by the shift means, and is otherwise separated. However, in the apparatus of the present embodiment, the transfer roller 25 is the intermediate transfer roller. The roller 25 is always in contact with the roller 25. Therefore, a shock or the like at the time of contact with the intermediate transfer roller 20 is eliminated, and it is possible to reduce defects such as abrasion and scratches of the intermediate transfer roller 20.

To sequentially superimpose the first to fourth color toner images from the photosensitive drum 1 onto the intermediate transfer roller 20, the core metal 21 of the intermediate transfer roller 20 is transferred from the first bias power source 61 to the intermediate transfer roller 20. Polarity opposite to toner (+)
It is executed with the primary transfer bias applied. The applied voltage is +2 kV to 5 kV as in the first embodiment.

During the sequential primary transfer of images from the photosensitive drum 1 to the intermediate transfer roller 20, the transfer roller 25
A bias voltage having the same polarity (-) as the toner is applied to the core metal 26 from the second bias power source 30 for the transfer roller. Due to this bias voltage, an electric field that repels the toner image is generated from the transfer roller 25 to the intermediate transfer roller 20, and even if the transfer roller 25 is in contact with the intermediate transfer roller 20, the intermediate transfer roller 20 side with respect to the transfer roller 25. The transfer of the toner image is prevented.

At this time, if the transfer roller 25 is conductive,
A current flows from the intermediate transfer roller 20 to the transfer roller 25, and the primary transfer efficiency from the photosensitive drum 1 to the intermediate transfer roller 20 decreases. Therefore, the surface protection layer 28 on the surface of the transfer roller 25 has an insulating EPD of about 100 μm.
An M layer is formed so that no current flows. With such a configuration, the leakage of the primary transfer current to the transfer roller 25 side can be prevented, and the primary transfer efficiency can be improved.

After that, the secondary transfer of the toner image from the intermediate transfer roller 20 to the transfer material 24 as the second image carrier is performed by the first bias power source 3 to the core metal 26 of the transfer roller 25.
It is performed by applying a secondary transfer bias having a polarity (+) opposite to that of the toner from 1.

Other configurations and controls of the apparatus are similar to those of the apparatus of the first embodiment.

With the configuration described above, the transfer roller 25 is always in contact with the intermediate transfer body 20. Therefore, the transfer roller 25 is caused by a shock or the like when the transfer roller 25 is brought into contact with or separated from the intermediate transfer body 20. 25 and the intermediate transfer body 20 can be reduced in abrasion and scratches, and the transfer roller 25
It is possible to prevent the primary transfer current from leaking to the side and improve the transfer efficiency.

<Embodiment 3> (FIGS. 5 to 7) FIG. 5 is a schematic configuration diagram of the apparatus of this embodiment. In the present embodiment, the intermediate transfer roller cleaner 35 is eliminated from the apparatus of the second embodiment (FIG. 4), and the intermediate transfer roller 20 is cleaned by the photosensitive drum 1.

In the intermediate transfer roller 20, a medium resistance elastic layer 22 is formed on a cored bar 21, and carbon is dispersed on it to control the resistance value of 10 ¹⁰ to 10 ¹³ Ω · cm.
It is coated with A layer 23.

The cleaning of the intermediate transfer roller 20 is performed in the following procedure. That is, after the transfer material 24 passes through the secondary transfer nip portion N2 between the intermediate transfer roller 20 and the transfer roller 25 and the secondary transfer is completed, the core metal 21 of the intermediate transfer roller 20 and the core metal 26 of the transfer roller 25. To the second bias power source 62.30 that applies a bias having the same polarity (-) as the toner. By this bias switching, the transfer residual toner on the intermediate transfer roller 20 is returned to the surface of the photosensitive drum 1 and is collected by the cleaning device 14 to clean the intermediate transfer roller 20.

The transfer roller 25 has an intermediate transfer member 20.
A negative voltage higher than that of the transfer roller 25 is applied.
The toner attached to the upper part is also returned to the photosensitive drum 1 via the intermediate transfer body 20 and collected by the cleaning device 14 to be cleaned.

The transfer roller 25 has a two-layer structure in which a foamed EPDM layer 27 in which carbon is dispersed is provided on a core metal 26, and an insulating PFA layer is coated as a surface protective layer 28 on the surface layer. The reason why the surface layer is made of PFA is to prevent the leakage of the primary transfer current and to prevent the transfer roller 25 from being contaminated by providing an insulating coat as in the second embodiment.

When such a transfer roller 25 is constructed to have a high surface hardness, a hollow image as shown in FIG. 6 is likely to occur when the image is secondarily transferred from the intermediate transfer roller 20 to the transfer material 24.

Therefore, in this embodiment, as the developer, the volume average particle diameter is about 10 μm and the specific charge amount is about −25.
A non-magnetic mono-component spherical toner having a polymerization method of μc / gr is used and contains a low softening point substance in an amount of 5 to 30% by weight. Since spherical toner has a small area in contact with the roller surface, etc., it has a high releasability and hardly remains on the roller.
The transfer efficiency is high, and the occurrence of voids during transfer is small.

The shape of the toner is substantially spherical, and as shown in FIG. 7, it is also effective that the shape of the orthogonal projection image of the toner particles has a shape factor (SF-1) in the range of 100 to 110. high.

This shape factor SF-1 was measured by randomly sampling 100 toner particle images using a Hitachi FE-SEM (S-800), and the image information was made by Nicolet Corporation via an interface. Image analysis device (Lu
It is performed by introducing it into zex3), analyzing it, and calculating it from the formula shown in FIG.

With a toner shape having a toner shape factor SF-1 of more than 110, the shape gradually approaches an irregular shape from a spherical shape,
At the same time, the transfer efficiency is lowered and the image dropouts are worsened. Therefore, in this example, a non-magnetic one-component polymerized toner having a shape factor SF-1 of 100 to 110 was used.

The voids in the transfer of an image are largely influenced by the surface hardness of the transfer roller.
A material with high hardness such as a tube can be used as a coating material.

<Other Embodiments> Examples 1 to 3 above
Has been described using a system using a non-magnetic developer, but the present invention is not limited to this, and it goes without saying that the same effect can be obtained by using a magnetic developer.

The image forming process for the first image carrier 1 is not limited to the electrophotographic process and may be any suitable process.

Although the shape of the intermediate transfer member has been described as a roller shape, the present invention is not limited to this, and for example, a belt-shaped intermediate transfer member may be used.

As the material of the lower layer of the transfer roller, not only the foamed EPDM but also the elastic material such as silicon rubber, Teflon rubber, chloroprene rubber, and the like were mixed and dispersed with metal oxide such as carbon or zinc oxide to give conductivity. . It may be a solid or foamed layer.

The contact transfer member is not limited to the transfer roller 25,
It may be a belt-shaped body or any other suitable shape and form.

[0060]

As described above, after the image formed on the first image carrier is primarily transferred to the intermediate transfer member, it is secondarily transferred to the second image carrier using a contact transfer member. In the image forming apparatus, by providing the protective layer on the surface of the contact transfer member used for the secondary transfer, it becomes possible to reduce scratches and abrasions of the intermediate transfer member or the contact transfer member and improve the transfer efficiency.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic cross-sectional view showing the layer structure of the intermediate transfer roller.

FIG. 3 is a schematic cross-sectional view showing the layer structure of the transfer roller.

FIG. 4 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

FIG. 5 is a schematic configuration diagram of an image forming apparatus according to a third embodiment.

FIG. 6 is a diagram showing an example of a secondary transfer image with a void.

FIG. 7 is an explanatory diagram of a shape factor SF-1 of a developer (toner).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st image carrier (photosensitive drum) 20 intermediate transfer body (intermediate transfer roller) 24 2nd image carrier (transfer material) 25 contact transfer member (transfer roller) 28 surface protection layer

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Katsuhiko Nishimura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Masami Takeda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Co., Ltd. (72) Inventor, Sai Sai, 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tatsu, 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takushi Shibuya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasuo Yoda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masahide Hirai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tatsuya Nakamura 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Inc.

Claims (11)

[Claims] 1. An image formed on a first image carrier is transferred onto an intermediate transfer member, and then the second image carrier is pressed against the intermediate transfer member by a transfer member to form an image on the intermediate transfer member. An image forming apparatus for transferring an image to a side of a second image carrier, wherein the transfer member is provided with a surface protective layer. 2. The image forming apparatus according to claim 1, wherein the surface protection layer of the transfer member prevents the lower layer component from seeping out. 3. The image forming apparatus according to claim 1, wherein the surface protective layer of the transfer member is a polyurethane elastomer. 4. The resistance of the surface protective layer of the transfer member is 10 ¹⁰ to.
The image forming apparatus according to claim 1, wherein the image forming apparatus has 10 ¹³ Ω. 5. The image forming apparatus according to claim 1, wherein the resistance of the surface protection layer of the transfer member is insulating. 6. The image forming apparatus according to claim 5, wherein the insulating layer serving as the surface protective layer of the transfer member is a fluororesin layer. 7. The image forming apparatus according to claim 1, wherein the transfer member has a roller shape. 8. The image forming apparatus according to claim 1, wherein the intermediate transfer member has a roller shape. 9. The image forming apparatus according to claim 1, wherein the intermediate transfer member is a roller having a medium resistance elastic body layer as a surface layer. 10. The image forming apparatus according to claim 1, wherein the developer for the image formed on the first image carrier is a substantially spherical toner formed by a polymerization method. 11. The image forming apparatus according to claim 10, wherein the shape of the developer is in the range of 100 to 110 in terms of the shape factor SF-1.